1. Field of the Invention
The present invention relates to a gasket adapted to be interposed between a tank opening and a cap, and to a tank cap and tank opening-closing device employing the gasket.
2. Description of the Related Art
A tank cap of this kind known to date is an automotive fuel cap for closing a tank opening, with a closure body having a gasket of C-shaped cross section installed thereon, adapted to be screwed into a thread on the inside wall of the filler pipe (JP-A 53-20054). With the aim of improving ease of operation of this kind of fuel cap, it has been contemplated to reduce the tightening torque while assuring at a minimum a prescribed level of seal face pressure. As one technology for accomplishing this, it has been contemplated to reduce the area of contact of the gasket with the seal face of the tank opening (JP-A 2005-153661).
However, reducing the contact area produces the following problem. In recent years, it has been contemplated to switch from iron to stainless steel as the material for the filler pipe in order to improve corrosion resistance. With stainless steel filler pipes, when the rim of the mouth is produced through press forming, the seal face FNf tends to have a rough surface, owing to the workability of the material. If the contact area of the gasket with such a rough seal face is reduced, the problem of a loss of seal may result.